In-situ solid rocket motor propellant grain aging using gas

ABSTRACT

A method for non-destructively determining a mechanical property of a solid rocket motor propellant grain may comprise applying, via a gas, a force to a surface of the solid rocket motor propellant grain, wherein a deformation is formed on the surface of the solid rocket motor propellant grain in response to the applying, and measuring a pressure of the gas. This process may be performed over time to determine a lifespan of the propellant grain.

FIELD

The present disclosure relates generally to solid rocket motors, andmore particularly, to systems and methods for assessing propellant grainlifespan.

BACKGROUND

Rocket propellant grains rely on a polymer binder for their structuralintegrity. Changes to structural integrity may be described by a changein mechanical properties that, in part, determines the propellant grainlifespan. While the chemical composition of a polymer type affects theway it ages, the changes in propellant grain mechanical properties dueto polymer aging are a factor in determining propellant grain lifespan.One method of assessing the lifespan of a solid rocket motor is bydestructively disassembling the solid rocket motor to measure mechanicalproperties of the propellant grain.

SUMMARY

A method for non-destructively determining a lifespan of a solid rocketmotor propellant grain is disclosed, comprising applying a force to asurface of the solid rocket motor propellant grain via a gas, wherein adeformation is formed on the surface of the solid rocket motorpropellant grain in response to the application of the force, andmeasuring a pressure of the gas.

In various embodiments, the propellant grain is a solid mass with anexposed inner surface area defining a perforation in the interior of thesolid rocket motor propellant grain.

In various embodiments, the method further comprises determining thelifespan of the solid rocket motor propellant grain based upon thepressure of the gas.

In various embodiments, the method further comprises moving the gas intothe perforation, wherein the force is applied to the surface in responseto the gas being moved into the perforation of the solid rocket motorpropellant grain.

In various embodiments, the gas is pressurized in response to moving apre-determined number of moles of gas into the perforation, wherein thedeformation is formed in response to the gas being pressurized.

In various embodiments, a pre-determined number of moles of the gas ismoved into the perforation.

In various embodiments, the method further comprises calculating a valueof a mechanical property of the solid rocket motor propellant grainbased upon the deformation.

In various embodiments, the mechanical property comprises a bulkrelaxation modulus (k) calculated using equation

${k = \frac{P}{\frac{\Delta V}{V_{initial}}}},$where P is the measured pressure, ΔV is a change in volume of theperforation, and V_(initial) is a volume of the perforation before itexpands in response to the gas.

A method for non-destructively surveilling a mechanical property of asolid rocket motor propellant grain is disclosed, comprising applying afirst force to a surface of the solid rocket motor propellant grain at afirst time, wherein a first deformation is formed on the surface of thesolid rocket motor propellant grain in response to the applying thefirst force, measuring a first value of a relaxation modulus of thesolid rocket motor propellant grain based on the first deformation,applying a second force to the surface of the solid rocket motorpropellant grain at a second time, wherein a second deformation isformed on the surface of the solid rocket motor propellant grain inresponse to the applying the second force, and measuring a second valueof the relaxation modulus of the solid rocket motor propellant grainbased on the second deformation, wherein at least one of the first forceor the second force is applied to the surface by moving a gas into aperforation of the solid rocket motor propellant grain.

In various embodiments, the method further comprises comparing the firstvalue with the second value.

In various embodiments, the method further comprises predicting a futurevalue of the relaxation modulus based on a trend between the first valueand the second value.

In various embodiments, the method further comprises determining aremaining lifespan of the solid rocket motor propellant grain based on acomparison between the future value and a pre-determined designthreshold.

In various embodiments, the gas is pressurized in response to moving apre-determined number of moles of gas into the perforation.

In various embodiments, at least one of the first deformation or thesecond deformation is formed in response to the gas being pressurized.

In various embodiments, the first value of the relaxation modulus ismeasured by measuring a pressure of the gas.

In various embodiments, the first value of the relaxation modulus ismeasured based upon an initial volume of the perforation and a secondvolume of the perforation.

In various embodiments, the first value of the relaxation modulus iscalculated using an equation P₂V_(initial)=nRT, where R is a universalgas constant of the gas, T is a temperature of the gas, n is a number ofmoles of the gas, V_(initial) is an initial volume of the perforation,and P₂ is a measured pressure of the gas.

A solid rocket motor propellant grain arrangement is disclosed,comprising a case, a propellant grain disposed within the case, aperforation extending through the propellant grain, and a port in fluidcommunication with the perforation, wherein the perforation isconfigured to receive a gas via the port.

In various embodiments, the solid rocket motor propellant grainarrangement further comprises a conduit coupled to the port.

In various embodiments, the solid rocket motor propellant grainarrangement further comprises a pressure gauge in fluid communicationwith the perforation, via the port.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be understood, however, the following descriptionand drawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures.

FIG. 1 illustrates a cross section view of a solid rocket motorcomprising a propellant grain having a perforation, in accordance withvarious embodiments;

FIG. 2 illustrates a method for non-destructively surveilling amechanical property of a solid rocket motor propellant grain, inaccordance with various embodiments;

FIG. 3A and FIG. 3B illustrate plots of bulk relaxation modulus of apropellant grain versus time, in accordance with various embodiments;

FIG. 4 illustrates a method for non-destructively surveilling amechanical property of a solid rocket motor propellant grain, inaccordance with various embodiments;

FIG. 5 illustrate plots of bulk relaxation modulus of a propellant grainversus time, in accordance with various embodiments;

FIG. 6 illustrates sub-steps of the method of FIG. 2 and/or FIG. 4,including methods for applying a force (or pressure) to the propellantgrain, as well as calculating the mechanical property, in accordancewith various embodiments;

FIG. 7A illustrates a cross section view of the solid rocket motor ofFIG. 1 with a port in fluid communication with the hermetically sealedperforation, in accordance with various embodiments; and

FIG. 7B illustrates a cross section view of the solid rocket motor ofFIG. 7A with the perforation filled with a gas, the perforation havingexpanded in response to the pressurized gas, in accordance with variousembodiments.

DETAILED DESCRIPTION

The detailed description of various embodiments herein makes referenceto the accompanying drawings, which show various embodiments by way ofillustration. While these various embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that logical, chemical, and mechanical changes may be madewithout departing from the scope of the disclosure. Thus, the detaileddescription herein is presented for purposes of illustration only andnot of limitation. For example, the steps recited in any of the methodor process descriptions may be executed in any order and are notnecessarily limited to the order presented.

Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected,or the like may include permanent, removable, temporary, partial, full,and/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

With reference to FIG. 1, a solid rocket motor 100 is illustrated, inaccordance with various embodiments. Solid rocket motor 100 may comprisean aft end 190 and a forward end 192. Solid rocket motor 100 maycomprise a casing 102 extending between aft end 190 and forward end 192.In various embodiments, casing 102 may comprise a cylindrical geometry.Solid rocket motor 100 may comprise a nozzle 120 disposed at aft end190. Nozzle 120 may be coupled to casing 102. Solid rocket motor 100 maycomprise a solid rocket motor propellant grain (propellant grain) 110disposed within casing 102. In various embodiments, propellant grain 110may be comprised of a solid fuel, such as a pure fuel, inert without anoxidizer. For example, propellant grain 110 may comprise ahydroxyl-terminated polybutadiene (HTPB), a polymethyl methacrylate(PMMA), or a polyethylene (PE), among others. In various embodiments,propellant grain 110 may be comprised of a composite propellantcomprising both a fuel and an oxidizer mixed and immobilized within acured polymer-based binder. For example, propellant grain 110 maycomprise an ammonium nitrate-based composite propellant (ANCP) orammonium perchlorate-based composite propellant (APCP). Propellant grain110 may be a solid mass with an exposed inner surface area defining aperforation volume (also referred to herein as a perforation) in theinterior of the solid rocket motor. In this regard, propellant grain 110may comprise a perforation 112. Perforation 112 may be defined by a boreextending axially through propellant grain 110.

A mechanical property envelope may describe the minimum and maximumperformance values necessary for a propellant grain to function asdesigned. The calculated mechanical property envelope is typicallyderived from a series of tests to determine propellant failure limitsunder various loading conditions. When a propellant sample mechanicalproperty falls outside of the calculated envelope, the propellant grainservice life is at an end.

The mechanical properties of the propellant comprising the grain can bemeasured both immediately after curing and after an accelerated agingperiod. Typically, the measurements are performed on propellant samplesproduced simultaneously with the production of propellant grains.Accelerated aging of the propellant samples is usually achieved throughexposure to high temperatures for a duration of time designed to mimicthe passage of time. The mechanical properties of the propellant graincontained within the rocket motor are typically assumed to berepresented by the simultaneously produced propellant samples. Theservice life of the propellant grain is then assumed to be representedby the performance of the propellant samples subjected to acceleratedaging, with a conservative reduction to compensate for potentialvariation between propellant sample and propellant grain.

To validate the typical assumption that the propellant grain within therocket motor is accurately represented by the propellant samples, it maybe desirable to calculate mechanical properties of a propellant grain todetermine the health of the corresponding solid rocket motor. Typically,in order to determine the health of a plurality of solid rocket motors,a sacrificial solid rocket motor is disassembled using destructive meansto gain access to the propellant of the sacrificial solid rocket motorin order to take proper measurements. The sacrificial solid rocket motorwould typically be similar to the plurality of solid rocket motors(e.g., same type, age, storage conditions, etc.). Stated differently, asolid rocket motor is sacrificed in order to estimate the health of aplurality of similar solid rocket motors.

The present disclosure, as described herein, provides systems andmethods for non-destructively surveilling solid rocket motor propellantgrains for predicting the lifespan and the remaining lifespan of thesolid rocket motor.

With reference to FIG. 2, a method 200 for non-destructively surveillinga mechanical property of a solid rocket motor propellant grain isillustrated, in accordance with various embodiments. Method 200 includesapplying a first force to a surface of the propellant grain at a firsttime, wherein a first deformation is formed on the surface of thepropellant grain in response to the first force (step 210). Method 200includes calculating a first value of the mechanical property of thepropellant grain, based on the first deformation (step 220). Method 200includes applying a second force to the surface of the propellant grainat a second time, a second deformation formed on the surface of thepropellant grain in response to the second force (step 230). Method 200includes calculating a second value of the mechanical property of thepropellant grain, based on the second deformation (step 240). Method 200includes determining the remaining lifespan of the propellant grain,based on the first value and the second value (step 250) and throughcomparison of their values with the modeled performance minima and/ormaxima.

With combined reference to FIG. 1 and FIG. 2, step 210 and step 230 mayinclude applying a force to surface 114 of propellant grain 110. Theforce may be applied via a variety of devices and/or methods, as will bedescribed with further detail herein. Surface 114 may be an innersurface of propellant grain 110. Surface 114 may be a radially displayedinner surface of propellant grain 110. Surface 114 may defineperforation 112. Perforation 112 may comprise a bore formed throughpropellant grain 110. A deformation may be formed in propellant grain110 in response to the force. For example, a deformation may be formedin surface 114 in response to the force. Step 220 and step 240 mayinclude calculating a mechanical property of propellant grain 110, basedupon the respective deformations. For example, a mechanical propertythat may be calculated is the bulk relaxation modulus (k) of propellantgrain 110. As will be described with further detail herein, the amountof deformation of the propellant grain 110 in response to a given force,may indicate the magnitude of the bulk relaxation modulus (k) ofpropellant grain 110.

In various embodiments, step 210 may occur at a first time and step 230may occur at a second time. Similarly, step 220 may occur during thefirst time and step 240 may occur during the second time. For example,step 230 and step 240 may occur a year or more after step 210 and step220. In this regard, the health of solid rocket motor 100 may besurveilled over a period of time. With additional reference to FIG. 3A,a plot 300 of various bulk relaxation modulus (k) values calculated overtime is illustrated, in accordance with various embodiments. Forexample, first value 302 may be calculated at a first time, second value304 may be calculated at a second time, and third value 306 may becalculated at a third time. A trend (also referred to herein as a curve)310 may be determined based on first value 302, second value 304, andthird value 306. For example, a curve of best fit (i.e., curve 310) maybe determined using any suitable method including, but not limited to,interpolation, polynomial interpolation, smoothing, line fitting, curvefitting, extrapolation, analytic models, etc. Although illustrated ashaving three separate values, it is contemplated that curve 310 may bedetermined using two or more values. For example, using solely firstvalue 302 and second value 304, or using more than three values.

Curve 310 may be used to determine a future value 309. For example,curve 310 may be compared with a pre-determined threshold value 320 ofbulk relaxation modulus (k) and a time 392 at which curve 310 willintersect with pre-determined threshold value 320 may be used to definefuture value 309. In this regard, curve 310 may be extrapolated toestimate a time 392 at which the mechanical property (e.g., bulkrelaxation modulus (k)) will reach the pre-determined threshold value320. Value 320 can be determined by modeling and calculation, throughmeasurement of propellant samples subjected to accelerated aging, or bydestructive testing of a sacrificial solid rocket motor. In this regard,it may be determined that solid rocket motor 100 has a lifespan ofduration 380. Duration 380 may be measured in units of time, such asyears, months, or days, for example.

With reference to FIG. 3B, a plot 301 of various bulk relaxation modulus(k) values calculated over time is illustrated, in accordance withvarious embodiments. Plot 301 differs from plot 300 of FIG. 3A in thatthe propellant grain bulk relaxation modulus (k) of plot 301 increasesover time. Thus, methods described herein may be suitable for propellantgrains that have a bulk relaxation modulus (k) that increase or decreaseover time. Stated differently, methods described herein may be suitablefor propellant grains that soften or harden over time.

Having described a method for non-destructively surveilling a mechanicalproperty of a solid rocket motor propellant grain using two measuredvalues, it is contemplated herein that a method for non-destructivelysurveilling a mechanical property of a solid rocket motor propellantgrain may be performed using only a single measured value. Withreference to FIG. 4 a method 400 for non-destructively surveilling amechanical property of a solid rocket motor propellant grain isillustrated, in accordance with various embodiments. Method 400 includesapplying a force to a surface of the propellant grain, wherein adeformation is formed on the surface of the propellant grain in responseto the force (step 410). Method 400 includes calculating a value of amechanical property of the propellant grain, based on the deformation(step 420). Method 400 includes determining the remaining lifespan ofthe propellant grain, based on the calculated value and a predeterminedtrend (step 430).

With combined reference to FIG. 1 and FIG. 4, step 410 may includeapplying a force to surface 114 of propellant grain 110. Step 420 mayinclude calculating a mechanical property of propellant grain 110, basedupon the deformation. For example, a mechanical property that may becalculated is the bulk relaxation modulus (k) of propellant grain 110.Step 430 may include comparing the calculated bulk relaxation modulus(k) of propellant grain 110 with a predetermined trend which representsthat of propellant grain 110, for example using a trend representing theperformance (i.e., bulk relaxation modulus) of a propellant samplesubjected to an accelerated aging process, or a trend calculated using amodel produced by the structural analysis of the propellant grain. Invarious embodiments, the predetermined trend is determined by modelingand calculation, through measurement of propellant samples subjected toaccelerated aging, and/or by destructive testing of a sacrificial solidrocket motor

With additional reference to FIG. 5, a plot 500 of a calculated bulkrelaxation modulus (k) value with respect to a predetermined trend isillustrated, in accordance with various embodiments. For example, value504 may be calculated and compared with a predetermined trend (alsoreferred to herein as a curve) 510 representing the change in bulkrelaxation modulus of the propellant grain with respect to time. Curve310 may be used to determine a future value 309. Curve 510 may becompared with a pre-determined threshold value 520 of bulk relaxationmodulus (k) and a future time 592 at which curve 510 will intersect withpre-determined threshold value 520 may be used to define future value509. In this regard, calculated value 504 may be superimposed with curve510 to estimate a time 592 at which the mechanical property (e.g., bulkrelaxation modulus (k)) will reach the pre-determined threshold value520. Value 520 can be determined by modeling and calculation, throughmeasurement of propellant samples subjected to accelerated aging, and/orby destructive testing of a sacrificial solid rocket motor. In thisregard, it may be determined that solid rocket motor 100 has a remaininglifespan of duration 580. Duration 580 may be measured in units of time,such as years, months, or days, for example.

Having described methods for non-destructively surveilling a mechanicalproperty of a solid rocket motor propellant grain for determining alifespan of a solid rocket motor, FIG. 6 through FIG. 7B illustratevarious methods for applying a force to the propellant grain, as well ascalculating the mechanical property.

With reference to FIG. 6, step 210 and/or step 230 of method 200 of FIG.2 and/or a step 410 of method 400 of FIG. 4 may include moving a gasinto a perforation (sub-step 630). Step 220 and/or step 240 of method200 of FIG. 2 and/or a step 420 of method 400 of FIG. 4 may includemeasuring a pressure of the gas (sub-step 630). Step 220 and/or step 240of method 200 of FIG. 2 and/or a step 420 of method 400 of FIG. 4 mayinclude calculating a mechanical property of the propellant grain, basedon the pressure (sub-step 640).

With respect to FIG. 7A and FIG. 7B, elements with like elementnumbering, as depicted in FIG. 1, are intended to be the same and willnot necessarily be repeated for the sake of clarity.

With reference to FIG. 7A, perforation 112 may be hermetically sealed atboth axial ends thereof. In this regard, a first end 702 of perforation112 may be sealed via a seal 706. Seal 706 may comprise any suitablehermetic seal, including rubber plugs, or glass-to-metal hermetic seals,among others. Seal 706 may be coupled to propellant grain 110 such thatpressurized gas does not leak from perforation 112. Furthermore, secondend 704 of perforation 112 may be hermetically sealed. The forward endwall 708 of casing 102 at second end 704 may hermetically sealperforation 112. In various embodiments, forward end wall 708 includesan ignitor for igniting propellant grain 110.

In various embodiments, solid rocket motor 100 includes a port 710 influid communication with perforation 112. With combined reference toFIG. 6A and FIG. 7A, sub-step 620 may include connecting a conduit 732,such as a hose for example, to port 710. Perforation 112 may comprise aninitial volume (V_(initial)). With combined reference to FIG. 6A andFIG. 7B, sub-step 620 may include moving a gas 735 into perforation 112.Gas 735 may be any compressible gas including air, nitrogen, etc. A gassupply 770 may be connected to conduit 732 to supply the gas 735 toperforation 112. In various embodiments, gas supply 770 may comprise agas cylinder. In various embodiments, sub-step 620 may include moving apre-determined number of moles of gas 735 into perforation 112. Thus,gas 735 may be moved into perforation 112 in a controlled manner.Perforation 112 may expand in response to the gas 735 being moved intoperforation 112. In this manner, all radial expansion of perforation 112may correspond to deformation of propellant grain 110. For example, gas735 may exert a force, depicted by arrows 795, on surface 114 which maycause surface 114 to expand. Force 795 may be exerted onto surface 114of propellant grain 110 in response to gas 735 being moved intoperforation 112. Thus, perforation 112 may comprise a volume (V₂) inresponse to being filled with gas 735. In this regard, a change involume of perforation 112 may correspond to a volume of the deformation.The change in volume of perforation 112 may correspond to a mechanicalproperty of propellant grain 110, such as the bulk relaxation modulus(k) of propellant grain 110 for example. Force 795 may be a relativelysmall force, causing a relatively small deformation, such that thedeformation does not damage the performance of propellant grain 110.

Sub-step 630 may include measuring a pressure (P₂) of gas 735. Apressure gauge 772 may be used to measure pressure (P₂). In this regard,pressure gauge 772 may be in fluid communication with perforation 730.Pressure (P₂) may be the pressure of a pre-determined number of moles ofgas 735 in perforation 730. The pressure (P₂) may vary in response tothe bulk relaxation modulus (k) of propellant grain 110. For example,bulk relaxation modulus (k) may be defined per equation 1 below:

$\begin{matrix}{k = \frac{P}{\frac{\Delta V}{V_{initial}}}} & {{EQ}.\mspace{14mu} 1}\end{matrix}$where k is the bulk relaxation modulus, P is the pressure applied by gas735 to propellant grain 110, ΔV is the change in volume of perforation730, and V_(initial) is the initial volume of perforation 730 beforeexpansion, such as is shown in FIG. 7A for example. In this regard,force 795 may be the product of pressure (P) and the area of theperforation 730 in contact with surface 114.

In this regard, ΔV may be defined by equation 2 below:ΔV=V _(initial) −V ₂  EQ. 2where V₂ is the volume of perforation 730 after being filled with thepre-determined number of moles of gas 735.

In various embodiments, the initial volume (V_(initial)) is a knownvalue. In various embodiments, the initial volume (V_(initial)) iscalculated by moving a known number of moles of gas (n), at a knowntemperature (T) into perforation 730 at a low, measured pressure(P_(meas)) (i.e., low enough such that the volume of perforation 730does not increase in response to the low pressure), and calculating Vusing equation 3 below.

Using the known initial volume, the expected pressure (P_(calc)) of gas735 can be determined using equation 3:P _(calc) V=nRT  EQ. 3where R is the universal gas constant of gas 735, T is the temperatureof gas 735, n is the number of moles of gas 735, and V is the initialvolume (V_(initial)) of perforation 112. The expected pressure(P_(calc)) is then compared with the measured pressure (P₂) and thedifference in pressures (i.e., P_(calc)−P₂) is noted. The differencefrom ideality is due to the compression of the propellant grain 110under pressure of gas 735. Stated differently, the calculated pressure(P_(calc)) and the measured pressure (P₂) may be slightly different forcontrolled additions of gas (varying n) in response to the propellantgrain being compressed which in turn will create a slightly largervolume (and reduced pressure) for the gas 735 to occupy. The differencebetween calculated pressure (P_(calc)) and the measured pressure (P₂)may be used to determine the remaining lifespan of propellant grain 110.In this regard, the Y-axis of FIG. 3A, FIG. 3B, and FIG. 5 may be“pressure (P₂)” instead of “modulus” or pressure difference(P_(calc)−P₂) instead of “modulus.” However, it is understood hereinthat, in various embodiments, the pressure (P₂) corresponds to themodulus of propellant grain 110. In this regard, the modulus ofpropellant grain 110 may be calculated based upon the measured pressure(P₂).

In various embodiments, the ambient temperature and atmospheric pressureis known so that any change in temperature or atmospheric pressurebetween calculation may be taken into account.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”,“various embodiments”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to invoke 35 U.S.C. 112(f) unlessthe element is expressly recited using the phrase “means for.” As usedherein, the terms “comprises”, “comprising”, or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A method for non-destructively determining alifespan of a solid rocket motor propellant grain, wherein the solidrocket motor propellant grain is a solid mass with an exposed innersurface defining a perforation in the interior of the solid rocket motorpropellant grain, the method comprising: applying a force to the innersurface of the solid rocket motor propellant grain via a gas, wherein adeformation is formed on the inner surface of the solid rocket motorpropellant grain in response to the application of the force; measuringa pressure of the gas; calculating a value of a mechanical property ofthe solid rocket motor propellant grain based upon a change in volume ofthe perforation and the pressure of the gas; and determining thelifespan of the solid rocket motor propellant grain based upon the valueof the mechanical property.
 2. The method of claim 1, furthercomprising: moving the gas into the perforation, wherein the force isapplied to the inner surface in response to the gas being moved into theperforation of the solid rocket motor propellant grain.
 3. The method ofclaim 2, wherein the gas is pressurized in response to moving apre-determined number of moles of gas into the perforation, wherein thedeformation is formed in response to the gas being pressurized.
 4. Themethod of claim 3, wherein a pre-determined number of moles of the gasis moved into the perforation.
 5. The method of claim 1, wherein themechanical property comprises a bulk relaxation modulus (k) calculatedusing equation ${k = \frac{P}{\frac{\Delta V}{V_{initial}}}},$ where Pis the measured pressure, ΔV is the change in volume of the perforation,and V_(intitial) is a volume of the perforation before it expands inresponse to the gas.
 6. A method for non-destructively surveilling amechanical property of a solid rocket motor propellant grain,comprising: applying a first force to a surface of the solid rocketmotor propellant grain at a first time, wherein a first deformation isformed on the surface of the solid rocket motor propellant grain inresponse to the applying the first force; measuring a first value of arelaxation modulus of the solid rocket motor propellant grain based onthe first deformation; applying a second force to the surface of thesolid rocket motor propellant grain at a second time, wherein a seconddeformation is formed on the surface of the solid rocket motorpropellant grain in response to the applying the second force; andmeasuring a second value of the relaxation modulus of the solid rocketmotor propellant grain based on the second deformation, wherein at leastone of the first force or the second force is applied to the surface bymoving a gas into a perforation of the solid rocket motor propellantgrain.
 7. The method of claim 6, further comprising comparing the firstvalue with the second value.
 8. The method of claim 7, furthercomprising predicting a future value of the relaxation modulus based ona trend between the first value and the second value.
 9. The method ofclaim 8, further comprising determining a remaining lifespan of thesolid rocket motor propellant grain based on a comparison between thefuture value and a pre-determined design threshold.
 10. The method ofclaim 6, wherein the gas is pressurized in response to moving apre-determined number of moles of gas into the perforation.
 11. Themethod of claim 10, wherein at least one of the first deformation or thesecond deformation is formed in response to the gas being pressurized.12. The method of claim 11, wherein the first value of the relaxationmodulus is measured by measuring a pressure of the gas.
 13. The methodof claim 12, wherein the first value of the relaxation modulus ismeasured based upon an initial volume of the perforation and a secondvolume of the perforation.
 14. The method of claim 11, wherein the firstvalue of the relaxation modulus is calculated using an equationP₂V_(initial)=nRT, where R is a universal gas constant of the gas, T isa temperature of the gas, n is a number of moles of the gas, V_(initial)is an initial volume of the perforation, and P₂ is a measured pressureof the gas.
 15. A solid rocket motor propellant grain arrangement,comprising: a case; a propellant grain disposed within the case; aperforation extending through the propellant grain, wherein theperforation is hermetically sealed at each of its axial ends; and a portin fluid communication with the perforation, wherein the perforation isconfigured to receive a gas via the port while the perforation remainshermetically sealed so as to expand the perforation.
 16. The solidrocket motor propellant grain arrangement of claim 15, furthercomprising a conduit coupled to the port.
 17. The solid rocket motorpropellant grain arrangement of claim 16, further comprising a pressuregauge in fluid communication with the perforation, via the port.